The aims are: 1. To identify, characterize and clone the pituitary receptor for growth hormone releasing factor (GRF). 2. To map the distribution of GRF receptors and mRNA throughout the body and test factors that may regulate GRF receptor message. 3. To perform structure/function studies that will reveal how receptor structure determines hormone selectivity and signal transduction. GRF is a peptide hormone released by the hypothalamus which acts on receptors in the anterior pituitary to stimulate the release of growth hormone. GRF is a member of the glucagon/secretin/VIP peptide family and is the major positive modulator controlling growth hormone release. Because of GRF's homology to VIP and secretin (whose receptors have recently been cloned) and because of the GRF receptor's sensitivity to GTP, the GRF receptor (GRF-R) is thought to be a member of the large family of G-protein coupled receptors with seven transmembrane spanning segments. The proposed experimental plan is to isolate and purify the receptor as a stable receptor-ligand complex, and to obtain amino acid sequences from receptor peptides. We have purified test amounts of the GRF receptor and have obtained a partial length cDNA clone by screening a human somatotroph tumor cDNA library for secretin receptor-like sequences. This sequence is similar to the VIP and secretin receptors and may be the GRF-R. Data suggests that we have found the full length of this cDNA clone. This clone will be sequenced and if it encodes a complete receptor we will test for GRF binding after transient expression in COS cells. The isolation and cloning of the GRF receptor and its in vitro expression will be of major importance in: 1. Understanding the receptors mechanism of action and its regulation. 2. Mapping the distribution of GRF receptors throughout the body and examining their physiological role outside the pituitary (if any). 3. Understanding its evolutionary relation to other G protein-linked receptors, especially others in the glucagon/secretin/VIP family. 4. Screening large numbers of analogs and xenobiotics for GRF activity. This could lead to improved agonists for use in clinical therapy to augment growth hormone secretion. This screening, together with modeling based on receptor structure, could lead to orally active nonpeptide GRF agonists that would be useful in medical practice and also in the development of higher yield milk production and higher yield, leaner livestock.